A printer generally holds a page memory for the purpose of recovery from an error such as a jam, and when an error occurs, error recovery is done using print data stored in the page memory.
However, error recovery cannot be achieved unless the printer holds a memory of a capacity capable of holding print data of at least two pages in order to perform double-sided printing by this method. Printing at the highest print speed of a printer engine generally requires a memory of a capacity capable of holding print data of four or eight pages. A high-resolution printer or color printer with a large data size needs a large-capacity memory in order to hold print data, raising the printer cost.
To solve this problem, there has conventionally been known a technique of suppressing the memory of a printer to a small capacity by equipping a page memory for error recovery with a host apparatus.
In double-sided printing by a printer which performs face-down delivery, like a general page printer, printing is first done on the back side (even-numbered page) and then the front side (odd-numbered page) so as to arrange a bundle of delivered paper sheets in the page order. Pages are printed in an order of 2, 1, 4, 3, . . . in double-sided printing of so-called 1-sheet retention, and an order of 2, 4, 1, 6, 3, . . . in double-sided printing of so-called 2-sheet retention by alternate paper feed.
This method, however, does not change the page transmission order in accordance with the print order, and requires an extra memory for double-sided printing on the printer side. For example, in double-sided printing of 1-sheet retention, pages are transmitted in an order of 1, 2, 3, 4, . . . , and after data of the first page is stored in the printer, data of the second page is received to start printing from the second page. The printer requires at least a memory capacity capable of holding print data of at least two pages.